It is known to provide a beam axle suspension system for a vehicle. In a vehicle such as an automotive vehicle, the beam axle suspension system may be a five-link beam axle arrangement between a frame and wheels or tires of the vehicle. The beam axle arrangement typically includes a beam axle, upper and lower links, a track bar, and a spring and damper unit. In this arrangement, the beam axle extends between a pair of wheels and is located cross car via the lateral track bar. The beam axle is located fore and aft via the upper and lower links. The upper and lower links also locate the beam axle torsionally. The vertical location of this beam axle is located via the spring and damper unit. Other suspension arrangements may have the spring and damper as separate units.
Beam axle suspensions utilize specific links with rubber isolators such as bushings that are arranged to control the suspension's location throughout the suspension's travel during use. A rear suspension link geometry, and the fore/aft and lateral stiffness, controlled by the bushing characteristics, alter the tire's attitude relative to a road surface. The attitude of the tire relative to the road surface influences the steer characteristics caused by irregularities in the road surface. Further, the rubber bushings, at attachment points, allow for isolation and damping of road surface induced loads and vibrations. The stiffness characteristics of these rubber bushings can be modified to allow for controlled movement of the suspension system during specific events to alter ride, handling, and isolation characteristics of the vehicle. Fore/aft, yaw, and lateral deflection characteristics of the suspension system have a significant impact on the handling and ride behavior of the vehicle.
All suspension systems are a compromise of cost, mass, packaging, and deflection characteristics. Generally, minimal levels of suspension yaw deflection, while the wheels travel over a road disturbance, is desired. Any yaw of the beam axle while driving over a road disturbance, steers the rear wheels, and correspondingly causes the vehicle to change the direction of its path. This amount of steer due to yaw should be controlled.
The amount of geometric steer of the beam axle due to lateral loading or displacement of the wheel vertically is carefully designed into a vehicle's rear suspension system in order to meet desired handling performance characteristics. In order to achieve the desired levels of steer, the geometry of the locating links of the beam axle is modified. The link geometry of a typical beam rear axle is compromised by physical interference of the links to other components and systems of the vehicle. In a typical five-link arrangement, it is desired to have the forward attachment of the lower fore/aft links placed far outboard. However, this link geometry tends to interfere with traditional vehicle frame structure. The other alternative is to move the rearward bushing attachment at the beam axle inboard. However, this results in the beam axle having very low yaw stiffness, which causes steer effects of the beam axle when the wheel travels over road disturbances due to the fore/aft loading of the wheels.
Further, it is generally desired to have low fore/aft beam stiffness to absorb energy while the wheels are traveling over a disturbance in the road (e.g., bump). It is further desired to have high lateral stiffness in the beam suspension in order to generate good handling characteristics of the vehicle. With traditional link orientations, the fore/aft stiffness is higher than desired in order to achieve the desired level of yaw and lateral stiffness.
Previous beam axle implementations have compromised beam yaw stiffness, lateral force stiffness, and fore/aft stiffness. The compliances are highly coupled, and modifying one stiffness mode for a desired vehicle performance characteristic alters one of the other compliance modes in an undesirable manner. This coupling necessitates a compromise between other compliance modes. The fore/aft, yaw, and lateral deflection characteristics of a rear suspension have a significant impact on the handling, ride and noise and vibration behavior of the vehicle.